Police detained several demonstrators trying to attract attention to their own causes, escorting a elderly woman wearing a paper hat labelled "Injustice" away from the court in Jinan.

"I want to see if China's courts are fair or not. Are they only unfair to people like us or to everyone?" said another woman, Lin Xiuli, 43.

Lin said she had applied to attend Bo's trial, and came to see "what the difference is between cases for top officials and for us regular people".

Bo, once one of China's highest-flying politicians, is set to go on trial Thursday for bribery and abuse of power.

Attendance at the proceedings -- which analysts say are meant to bring to a close a scandal which exposed deep divisions and corruption at the highest levels of the Communist Party -- is likely to be strictly controlled, with independent media barred from entry.

The protester detentions occurred in front of a gaggle of reporters -- kept away from the courthouse by a cordon -- while more demonstrators arrived later.

Several identified themselves as petitioners -- citizens with decades of personal grievances who file complaints with more senior departments, but often face illegal detention.

Lin said she had been petitioning for eight years over a civil case involving an ex-boyfriend, and had been detained more than 20 times for a total of more than 900 days.

She and four other protesters had a noisy row with police, while another group who said they travelled to the courthouse from China's commercial hub Shanghai hurriedly handed papers to journalists and called out as police ushered them away.

The extremely sensitive trial has been anticipated for around a year and a half, since Bo was dismissed from his position as head of the megacity of Chongqing and as a member of the ruling Communist Party's 25-strong Politburo.

He is almost certain to be found guilty and face a hefty jail sentence, with the result of the trial decided by backroom political bargaining, analysts say.

About 50 police practised drills in the morning on the grounds of the courthouse, a broad and stately structure with a Chinese flag at its entrance. They worked with sniffer dogs and a few wore bullet-proof vests.

On a small bulletin board on the side of the courthouse was a short stamped notice announcing: "This court is scheduled to hold the open trial for the bribery, corruption and abuse of power case of the defendant Bo Xilai on August 22 at 8:30 at Courtroom No 5."

A few passers-by stopped to read the announcement before walking quietly away.